Traditionally, a passive dynamic damper composed of an auxiliary mass such as a weight, a spring element, and a damper element is known as a damping device that suppresses vibrations. Although it has a simple configuration, the passive dynamic damper can advantageously reduce vibrations corresponding to the excitation frequency component generated in an object to be damped theoretically to zero by matching the natural frequency of the dynamic damper alone with the excitation frequency to set damping to zero.
To obtain a good damping performance with the passive dynamic damper, however, a task is required to finely adjust the spring constant and the damping coefficient, which are of the spring element and the damper element, respectively.
Accordingly, active damping devices have been invented and in practical use. The active damping devices create effects of a spring and a damper by means of an actuator, facilitating adjustment for the spring constant and the damping coefficient to provide desired stiffness and damping characteristics without the need of mechanical adjustment for the spring element itself or the damper element itself. To date, the applicant has also proposed active damping devices capable of suppressing vibrations of an object to be damped depending on an excitation frequency component of an excitation source (such as an engine) by means of a reaction force produced when an auxiliary mass is driven by a reciprocating linear actuator (Patent Literature 1, and the like).